Possession Island is located 1.6 km from the Diamond Coast of south-western Namibia, just south of Elizabeth Bay, c.40 km south of Lüderitz. This rectangular island is the largest of Namibia’s guano islands. It extends 4 km from north to south and is at most 1 km wide. Low rainfall (less than 10 mm per year) and frequent storms inhibit vegetation growth, and isolated bushes are scattered around otherwise barren and somewhat sandy ground. Old diamond diggings have broken much of the sandy surface. The island still holds a main jetty and the remains of a small village. Like the other guano islands it was stripped of its guano cap in the 1840s and has never regained it. It is permanently manned to keep seals from settling on the island.
See Box for key species. As Possession Island is the largest of the Namibian coastal islands, it has the potential to hold the most seabirds. This honour, however, goes to Ichaboe (IBA NA016) which is 14 times smaller than Possession. Despite the relatively low seabird densities, Possession Island is a vitally important coastal seabird breeding island, supporting over 20,000 seabirds in total. Important species include decreasing numbers of Spheniscus demersus, Morus capensis, Phalacrocorax capensis, P. coronatus and P. neglectus (10 pairs). Some of these breeding seabirds have been in decline since the island was first surveyed in 1956. Numbers of Spheniscus demersus decreased by 92% and numbers of Morus capensis by 68% over the next 40 years. While some colonies have disappeared altogether, others remain at much-reduced densities. Single pairs are unusual, scattered haphazardly over barren portions of the island. Large areas which were once occupied by breeding birds, now stand unused. This is the only island breeding site of the normally mainland-breeding Sterna balaenarum. Small colonies of Sterna balaenarum, that once bred between dunes on the adjacent mainland, have largely disappeared since the early 1970s. Sterna bergii are said to have nested on the island, but now no longer do. Haematopus moquini are common on the island.
Non-bird biodiversity: Of great significance was the birth of a calf of Eubalaena australis (LR/cd) in Elizabeth Bay in 1996, the first breeding record of this whale on the Namibian coast for over 100 years.
BirdLife International (2019) Important Bird Areas factsheet: Possession Island. Downloaded from http://www.birdlife.org on 23/08/2019.